Inhibitor



Patented Nov. 5, 1929 UNITED STATES PATENT OFFICE LUDWIG J. CHRISTMANN,.OF JERSEY CITY, NEW JERSEY, ASSIGNOR TO AMERICAN CYANAMIID COMPANY, OFNEW YORE, N. Y., A CORPORATION OF MAINE INHIBITOR No Drawing.

This invention relates to methods of cleaning or pickling metals bysubjecting the same to an acid bath.

In the me'tal industries, particularly in the manufacture of iron orsteel sheets or the like, which are to be coated with protective metalssuch as zinc, tin or cadmium, it is a common expedient to first cleanthe metal surface in order that the subsequent coating materialmayadhere firmly thereto, without danger of peeling off of the coating.This cleaning treatment usually consists in providing a dilute solutionof a non-oxidizing mineral acidmaterial, such as sulphuric acid,

called a pickling bath, and immersing the metal articles to be cleanedin the bath for a length of time sufiicient to remove scale, oxide andother matter from the surface of the metal. The bath is usuallymaintained at a predetermined temperature, usually above roomtemperature, during the pickling operation.

The acid in the pickling bath not only acts to remove the undes rablesurface materials but also tends to attack the metal itself and, toprotect the metal from attack by the acid, there is usually added to thepickling bath a small amount of a substance called an inhibitor. Theinhibitor permits the acid to remove the undesirable surface materialfrom the metal and prevents, either in whole ,or in part, the action ofthe acid upon the metal itself. Ordinarily, in the absence of aninhibitor, the acid in attacking the metal gives off a substantialquantity of hydrogen or other gaseous substances with the production ofan acid mist or spray which is injurious to the workmen and, inaddition, results in appreciable loss of acid.

The present invention is intended to provide an inhibitor which may beprepared easily, which is low in cost and which is highly effective in apickling bath even.

though present in small amounts.

1 have discovered that thiobenzamide is highly effective as an inhibitorin a pickling bath. This material may be obtained in any suitable andwell known manner.

The inhibitor constituting the subject mat- Application filed September18, 1929. Serial No. 303,589.

ter of my invention was tested in a pickling bath in the followingmanner:

A pickling solution Was prepared consisting of 250 cc. of dilutesulphuric acid containing 6% by weight of 66 B. acid. The solution wasplaced in a suitable vessel, maintained at a temperature of l83185 F.and 0.100 grams of thiobenzamide was added to the solution. a This isequivalent to about 4 one-hundredths of one percent of inhibitor in thebath.

Strips 3 long and wide of30 gauge tin plate stock were used for thetests. The

specimens were first" cleaned with ether to remove any oil or grease onthe surface, and, after drying were immersed in the pickling bath forfive minutes to remove the oxide scale. The specimens were removed fromthe bath, dried and weighed. 'The'specimens were immediately returned tothe pickling bath, immersed for twenty minutes, washed, dried andweighed again. The loss in weight was determined and the specimens weresubjectedto another20 minute test. Throughout the tests, check runs weremade with similar pickling baths but without-using any inhibitor. Thetable given belowshows the results obtained with and withoutthiobenzamide in the pickling bath:

- Im- Immersed Per Per $2 mersed v20 min. cent cent ,5 20 min. more lossin loss in P loss total 20min. 40min.

loss

Grams Grams Grams No inhibltorin bath"--- 4.060 100.0Thl0beu1amide1nbath-. 4.014 0. 014 0.033 0.35 0.83

From the above it is clear that thiobenzamide is a good inhibitor andeflectively'curtails the action of the acid upon the meta-1.

This is particularly true in view of the fact .1 that the-sample pickledin the bath containing no inhibitor was so rapidly dissolved I A,

the acid that before the end of forty ni in-"9'5" utes it was completelyin solution. There- I fore, no effort was made to weigh the checksamplesduring the tests. In similar tests carried out at higher and lowertemperatures, it was found that the thiobenaaf mide was equallyeffective as at temperatures originally described.

a non-oxidizing mineral acid Although I have described my invention insome detail, it is not l'imitedto the specific matters set forth. Theamounts of inhibitor used in pickling baths may, of course, be variedwldely and the nature of the bath may also be changed to suit anyparticular conditions which may prevail. In general, it is not necessaryto use more than 1% of inhibitor in the bath for most purposes less than0.1% is sufficient. It is to be understood that my invention is not tobe limited except as set forth in the claims appended hereto.

I claim:

1. A method of cleaning or pickling metals which comprises subjectingthe same to a pickling or cleaning bath containing a small amount ofthiobenzamide.

2. A method of cleaning or pickling metals which comprises subjectingthe same to a pickling bath'containing less than 1% of thiobenzamide.

3. A method of cleaning or pickling metals which comprises subjectingthe same to a pickling or cleaning bath containing less than 0.1% ofthiobenzamide.

4. A method of cleaning or pickling als which comprises subjecting thesame to a pickling or cleaning bath containing about 0.01% ofthiobenzamide.

' 5. A bath for pickling metals comprising a non-oxidizing mineral acidand a small amount of thiobenzamide. k

6. A bath for pickling metals comprising a non-oxidizingmineral acid andless than 1% of thiobenzamide. I

7 A bath for pickling metals comprising and less than 0.1% ofthiobenzamide.

8. A bath for pickling metals coin rising sulphuric acid and about-0.01%of t 'obenzamide.

- I In testimony whereof, I have hereunto subscribed my name this 16thday of September,

LUDWIG J. CHRISTMANN.

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